1. Field of the Invention:
The present invention relates to a photosensitive member comprising an overcoat layer on a photosensitive layer of organic materials.
2. Description of the Related Art:
Remarkable progress has been made in the application of electrophotographic techniques since the invention of the Carlson process. Various materials have also been developed for use in electrophotographic photosensitive members.
Organic materials used for the construction of electrophotographic photosensitive members are well known to those skilled in the art (for example, the materials disclosed in the Dec. 15, 1986 issue of Nikkei New Materials, pages 83-98), and these materials have made superior photosensitive members practical from the standpoint of sensitivity, chargeability and construction costs.
Materials used in the construction of organic photosensitive members are, in general, photoconductive materials which produce an electric charge such as, for example, phthalocyanine series pigments, azo series pigments, perillene series pigments and the like, electrical charge transporting materials such as, for example, triphenylmethanes, triphenylamines, hydrazones, styryl compounds, pyrazolines, oxazoles, oxydiazoles, and the like, binding materials for dispersion coating such as, for example, polyester, polyvinyl butyral, polycarbonate, polyarylate, phenoxy, styrene-acryl, and other resins.
Repeated use of these types of photosensitive members, however, gives rise to the problems of image defects, white streaks, and the like. These problems arise because the surface hardness of the organic photosensitive member roughly falls within the range from the 5B to the B levels of the JIS standards for pencil lead hardness, thus the surface of the photosensitive member is readily damaged due to the friction which is generated when the member comes into contact with the transfer paper, cleaning components, developer, and the like. Another cause of such problems is the harsh surface contact made when paper jams occur and the resultant reversion to manual operation required to remedy the malfunction. Furthermore, damage to the surface of the photosensitive member results in a marked reduction in the surface potential of the member.
In order to eliminate these disadvantages, it is proposed that the surface of the photosensitive member be covered with a protective layer.
Japanese Unexamined Patent Publication No. SHO 62-156664 discloses a photosensitive member comprising an amorphous silicon photoconductive layer and an overcoat layer of amorphous carbon containing fluorine atoms. When fluorine atoms are incorporated into the amorphous carbon overcoat layer, the member exhibits excellent resistance to humidity and durability. Our inventors have found that the member exhibits a more excellent resistance to humidity if fluorine atoms are incorporated in increasing amounts into the amorphous carbon overcoat layer.
However, when an organic photosensitive member having an overcoat layer containing fluorine atoms was installed in a copy machine for carrying out the copying operation, an image fog was observed at an initial stage. This image fog may be attributed to a large electronegativity of fluorine atoms present at the surface of the overcoat layer. Our inventors assume that, when the non-image portion formed on the member comprising the overcoat layer having fluorine atoms is in contact with the developer, the developer is positively charged with respect to a photosensitive drum in the triboelectric series due to the large electronegativity of fluorine atoms. Therefore, an electrostatic attraction is developed between the developer and fluorine atoms contained in the overcoat layer. As a result, the developer is deposited onto the non-image portion formed on the photosensitive member, producing the image fog.